Electron Spin Resonance across the Charge-ordering Transition in YBaMn2O6

TL;DR

This study uses electron spin resonance to explore the magnetic and charge-ordering transitions in YBaMn2O6, revealing how ESR parameters change across structural and charge-ordering phase transitions and providing insights into polaronic effects.

Contribution

First ESR investigation of YBaMn2O6 across charge-ordering and structural transitions, highlighting the role of polaronic hopping and charge fluctuations in the magnetic properties.

Findings

ESR parameters show jump-like changes at the structural transition T_t.

Charge-ordering manifests as a broad anomaly at T_CO.

ESR susceptibility indicates suppression of e_g-spin contribution due to polaronic hopping.

Abstract

We investigated the metal-ordered manganite system YBaMn2O6 using electron spin resonance (ESR) in the paramagnetic regime across the charge-ordering and structural phase transition at T_CO = 480 K and T_t = 520 K, respectively. All ESR parameters exhibit jump-like changes at T_t while the charge-ordering at T_CO manifests itself only as a weak and broad anomaly. Above T_t the ESR spin susceptibility is reduced with respect to the dc-susceptibility, indicating that only the t_2g-core spins of Mn ions contribute to the resonance absorption. The contribution of the e_g-spins is suppressed by the time scale of the polaronic hopping process of the e_g-electrons. The linewidth in this regime is reminiscent of a Korringa-type relaxation behavior. In this picture the ESR properties below T_t are dominated by the slowing down of the polaronic hopping process. The charge fluctuations persist down to the temperature T* ~ 410 K, below which the system can be described as a charge-ordered assembly of Mn$^{3+}$ and Mn$^{4+}$ spins.